There is known an overhead projector of which the support arm is bent and has at the bend a blower which produces a flow of cooling air through the support arm in which a part of the electronic power supply circuitry is accommodated and which at the same time produces a flow of cooling air in a second flow path past the objective in the projection head and light source in the projection head or horizontal portion of the support arm.
There is also known another overhead projector in which, for cooling of the Fresnel lens below the writing plate, the base plate is made hollow and a ventilator produces a flow of cooling air through the base plate beneath the Fresnel lens.
The accommodation of long, straight circuit boards on which the electronic components of the power supply circuitry are mounted in a wide straight support arm, presents no difficulty. However, if the support arm is bent and/or of such small cross section that the circuit boards of the electronic components cannot be accommodated in the support arm, there is difficulity in accommodating the power supply circuitry.
In another known embodiment of an overhead projector, the power supply circuitry is arranged in a rear part of the base plate in a region beyond the writing plate and directly adjacent the support arm. However, this arrangement requires a special housing for the power supply circuitry. This arrangement of the power supply circuitry has been found to be unsightly. Moreover, the power supply circuitry occupies space which could well be used as a storage surface for objects that are to be successively projected. Also, this arrangement of the power supply circuitry deprives the user of the overhead projector of a part of his viewing surface.